Optical systems and methods for biological analysis

ABSTRACT

An instrument for processing and/or measuring a biological process contains an excitation source, a sample holder, an optical sensor, an excitation optical system, and an emission optical system. The sample holder is configured to receive a plurality of biological samples. The optical sensor is configured to receive an emission from the biological samples. The excitation optical system is disposed along an excitation optical path and is configured to direct the electromagnetic radiation from the excitation source to the biological samples. The emission optical system is disposed along an emission optical path and is configured to direct electromagnetic emissions from the biological samples to the optical sensor. The instrument further contains a plurality of filter assemblies configured to be interchangeably located along at least one of the optical paths. The plurality of filter components includes a first filter assembly characterized by a first optical power and a first filter having a first filter function, the first filter function characterized by at least one of a first low-pass wavelength or a first high-pass wavelength. The second filter assembly is characterized by a second optical power and a second filter having a second filter function, the second filter function comprising at least one of a second low-pass wavelength that is different than the first low-pass wavelength or a second high-pass wavelength that is different than the first high-pass wavelength.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional application of U.S. application Ser.No. 14/348,878, filed Mar. 31, 2014, which is a 371 U.S. national phaseof international application no. PCT/US2012/058107, filed Sep. 28, 2012,which claims the benefit of priority of U.S. provisional applicationSer. No. 61/541,495, filed Sep. 30, 2011 (now expired), and U.S.provisional application Ser. No. 61/541,453, filed on Sep. 30, 2011 (nowexpired), which applications are incorporated herein by reference intheir entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates generally to systems, devices, and methodsfor observing, testing, and/or analyzing one or more biological samples,and more specifically to systems, devices, and methods comprising anoptical system for observing, testing, and/or analyzing one or morebiological samples.

Description of the Related Art

Optical systems for biological and biochemical reactions have been usedto monitor, measure, and/or analyze such reactions in real time. Suchsystems are commonly used in sequencing, genotyping, polymerase chainreaction (PCR), and other biochemical reactions to monitor the progressand provide quantitative data. For example, an optical excitation beammay be used in real-time PCR (qPCR) reactions to illuminatehybridization probes or molecular beacons to provide fluorescent signalsindicative of the amount of a target gene or other nucleotide sequence.Increasing demands to provide greater numbers of reactions per test orexperiment have resulted in instruments that are able to conduct everhigher numbers of reactions simultaneously.

The increase in the number sample sites in a test or experiment has ledto microtiter plates and other sample formats that provide ever smallersample volumes. In addition, techniques such as digital PCR (dPCR) haveincreased the demand for smaller sample volumes that contain either zeroor one target nucleotide sequence in all or the majority of a largenumber of test samples. The combination of small feature size (e.g., anindividual sample site or volume) and large field of view to accommodatea large number of test samples has created a need for optical systemsthat provide high optical performance with relatively small samplesignals.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention may be better understood from thefollowing detailed description when read in conjunction with theaccompanying drawings. Such embodiments, which are for illustrativepurposes only, depict novel and non-obvious aspects of the invention.The drawings include the following figures:

FIG. 1 is a schematic representation of a system according to anembodiment of the present invention.

FIG. 2 is a table of the filter functions for a plurality of filter usedin the emission filter assembly shown in FIG. 1

FIG. 3 is a table of the filter functions for a plurality of filter usedin the excitation filter assembly shown in FIG. 1

FIG. 4 is a top view of a sample holder and carrier according to anembodiment of the present invention.

FIG. 5 is a top view and magnified views of a sample holder according toanother embodiment of the present invention.

FIG. 6 is a perspective view of a sample holder according to yet anotherembodiment of the present invention.

FIG. 7 is a top view of a sample holder and carrier according to anotherembodiment of the present invention.

FIG. 8 is a graph showing the spectral output from an excitation sourceaccording to an embodiment of the present invention.

FIG. 9 is a cross-sectional view of a heated lid, sample holder, andcarrier according on an embodiment of the present invention.

FIG. 10 is a cross-sectional view of a heated lid, sample holder, andcarrier according on another embodiment of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

As used herein, the term “light” means electromagnetic radiation withinthe visible waveband, for example, electromagnetic radiation with awavelength in a vacuum that is within a range from 390 nanometers to 780nanometers. As used herein, the term “infrared” means electromagneticradiation having a wavelength within a range of 0.74 micrometer to 300micrometers.

As used herein, the term “optical power” means the ability of a lens oroptic to converge or diverge light to provide a focus (real or virtual)when disposed within air. As used herein the term “focal length” meansthe reciprocal of the optical power. As used herein, the term“diffractive power” or “diffractive optical power” means the power of alens or optic, or portion thereof, attributable to diffraction ofincident light into one or more diffraction orders. Except where notedotherwise, the optical power of a lens, optic, or optical element isfrom a reference plane associated with the lens or optic (e.g., aprincipal plane of an optic).

As used here, the term “about zero” or “approximately zero” means within0.1 of the unit of measure being referred to, unless otherwise noted.For example, “about zero meters” means less than or equal to 0.1 meters,if the dimension may only reasonably have a positive value, or within arange of −0.1 meters to +0.1 meters, if the dimension may have either apositive or negative value.

When used in reference to an optical power in units of Diopters, theterms “about” or “approximately”, as used herein, means within 0.1Diopter. As used herein, the phrase “about zero Diopter” or“approximately zero Diopter” means within a range of −0.1 Diopter to+0.1 Diopters.

Referring to FIGS. 1-3, a system or instrument 1000 for biologicalanalysis comprises an optical system 100. In certain embodiments, systemor instrument 1000 additionally comprises a sample block or processingsystem 200 and/or an electronic processor, computer, or controller 300configured to control, monitor, and/or receive data from optical system100 and/or sample processing system 200. Without limiting the scope ofthe present invention, system or instrument 1000 may be a sequencinginstrument, a polymerase chain reaction (PCR) instrument (e.g., areal-time PCR (qPCR) instrument and/or digital PCR (dPCR) instrument),an instrument for providing genotyping information, or the like.

In certain embodiments, optical system 100 comprises an illumination orexcitation source 110 providing one or more excitation beams 111 and anoptical sensor 118 configured to receive one or more emission beams 119from one or more biological samples 115. Optical system 100 alsocomprises an excitation optical system 120 and an emission opticalsystem 125. Excitation optical system 120 is disposed along anexcitation optical path 126 and is configured to direct theelectromagnetic radiation or light from excitation source 110 to sampleholder containing one or more biological samples. Emission opticalsystem 125 is disposed along an emission optical path 128 and isconfigured to direct electromagnetic emissions from biological samples115 to optical sensor 118, for example, one or more fluorescence signalsproduced at one or more wavelengths in response to the one or moreexcitation beams 111. Optical system 100 may further comprise anemission filter assembly 130 comprising a plurality of filtercomponents, elements, or modules 131 configured to interchangeablylocate or move one or more of filter modules 131 into emission opticalpath 128. Optical system 100 may additionally comprise an excitationfilter assembly 132 comprising a plurality of filter components,elements, or modules 133, wherein excitation filter assembly 132 isconfigured to interchangeably locate or move one or more of filtermodules 133 into excitation optical path 126. Optical system 100 mayfurther comprise a first optical element 152 configured to direct lightto optical sensor 118, a second optical element 154 configured to directexcitation light to, and/or emission light from, the biological samples,a beamsplitter 160, and/or one or more optical windows 162.

In certain embodiments, sample processing system 200 comprises a carrieror support frame 202 configured to receive a sample holder 204. Sampleholder 204 comprises a plurality or array of cells 205 for containing acorresponding plurality or array of biological samples 115 that may beprocessed by sample processing system 200 and/or optical system 100.Cells 205 may be in the forms of sample wells, cavities, through-holes,or any other chamber type suitable containing and/or isolating theplurality of biological samples 115. For example, sample cells 205 maybe in the form of sample beads in a flow cell or discrete samplesdeposited on top of a substrate surface such as a glass or siliconsubstrate surface.

With additional reference to FIG. 4, sample holder 204 comprises 96sample cells 205 that are in the form of 96 sample wells 209 configuredto provide 96 isolated or distinct biological samples 115.Alternatively, sample holder 204 may comprise less than 96 well andsamples, for example, 48 wells and samples, or may contain more than 96wells, for example, 384 or more wells and samples. In certainembodiments, carrier 202 is configured to receive more than one sampleholder 204 for simultaneous processing by sample processing system 200and/or optical system 100.

Sample processing system 200 may further comprise a block or assembly210 for receiving sample holder 204. Block 210 may be thermal blockincluding temperature control hardware for controlling or cycling thetemperature of biological samples 115. Sample processor system 200 mayfurther comprise a thermally controlled or heated lid 212 disposed aboutsample holder 204. Thermally controlled lid 212 may be configured to aidin controlling a thermal and/or humidity environment of biologicalsamples 115 or sample holder 204, for example, to aid in preventingcondensation from forming on samples 115 or optical elements of sampleholder 204. In certain embodiments, system 200 includes a set ofdifferent types or configurations of block 210 and/or different types orconfigurations of thermally controlled lid 212, where each member of theset is configured for use with a different type or number of sampleholders 204 or carriers 202.

Referring to FIG. 5, system 1000 may be additionally or alternativelyconfigured to receive and process a sample holder 304 comprising asubstrate 306 including a plurality of through-holes 309. In suchembodiments, through-holes 309 are configured to maintain isolated ordistinct biological samples 315 by capillary forces, for example, byforming through-holes to have an appropriately small diameter and/orthrough the use of hydrophilic and/or hydrophobic materials or coatings.Substrate 306 may further comprise an alphanumeric 320, a barcode 322,and/or similar symbol for identification or processing purposes.Referring to FIG. 6, sample holder 304 may further comprise an enclosureor case for protecting or sealing substrate 306 and the biologicalsamples contained in through-holes 309. The case may comprise a base 324and a cover 328 that are configured to seal substrate 306 between base324 and cover 328, for example, to reduce or prevent evaporation of thebiological samples. Cover 328 is made of a transmissive material andcomprises a top surface 330 and an opposing bottom surface 332 forproviding optical access to substrate 306. One or both surfaces 330, 332may comprise an antireflective coating, for example, to reduceretro-reflections of light from excitation beam 111 back toward opticalsensor 118. Additionally or alternatively, one or both surfaces 330, 332may be disposed at an angle relative to a front surface of substrate306, for example, to reduce retro-reflections of light from excitationbeam 111 back toward optical sensor 118. Referring to FIG. 7, one ormore sample holders 304 may be retained by or mounted on a carrier 302that is configured to be received by sample processing system 200. Inthe illustrated embodiment shown in FIG. 7, carrier 302 is configured toretain four or less sample holders 304. For clarity, not all thethrough-holes

In the illustrated embodiment shown in FIG. 5, each through-hole 309 hasa diameter of about 320 micrometers, a thickness of about 300micrometer, and a volume of about 33 nanoliters. Through-holes 309 havea nominal spacing in the illustrated embodiment of about 500 micrometerscenter to center. As discussed in greater detail below, optical system100 may be configured to allow imaging and processing of biologicalsamples contained in through-holes having such small diameters orvolumes. Additionally or alternatively, system 1000 and/or opticalsystem 100 is configured receive and process a sample holder 304 havingsmaller through-hole diameter and/or a smaller nominal spacing than inthe illustrated embodiment of FIG. 5. For example, optical system 100may be configured to allow system 1000 to receive and process a sampleholder 304 comprising through-holes having a diameter that is less thanor equal to 250 micrometer and/or a volume that is less than or equal to5 nanoliters. Alternatively, optical system 100 may be configured toallow system 1000 to receive and process a sample holder 304 comprisingthrough-holes having a diameter that is less than or equal to 150micrometer and/or a volume that is less than or equal to one nanoliter.

In certain embodiments, an initial sample or solution for a sampleholder, such as sample holders 204, 304, may be divided into hundreds,thousands, tens of thousands, hundreds of thousands, or even millions ofreaction sites, each having a volume of, for example, a few nanoliters,about one nanoliter, or less than one nanoliter (e.g., 10's or 100's ofpicoliters or less).

In the illustrated embodiments shown in FIGS. 4 and 5, sample holders204, 304 have a rectangular shape; however, other shapes may be used,such as a square or circular shape. In certain embodiments, a sampleholder such as sample holder 304 has a square shape and an overalldimension of 15 millimeter by 15 millimeter. In such embodiments, thesample holder may have an active area, region, or zone with a dimensionof 13 millimeter by 13 millimeter. As used herein, the terms “activearea”, “active region”, or “active zone” mean a surface area, region, orzone of a sample holder, such as the sample holders 204 or 304, overwhich reaction regions, through-holes, or solution volumes are containedor distributed. In certain embodiments, the active area of sample holder304 may be increased to 14 millimeter by 14 millimeter or larger, forexample, a 15 millimeter by 15 millimeter substrate dimension.

In the illustrated embodiment of FIG. 5, through-holes 309 may have acharacteristic diameter of 320 micrometer and a pitch of 500 micrometersbetween adjacent through-holes. In other embodiments, through-holes 309have a characteristic diameter of 75 micrometer and have a pitch of 125micrometers between adjacent through-holes. In yet other embodiments,through-holes 309 have a characteristic diameter of that is less than orequal 75 micrometers, for example, a characteristic diameter that isless or equal to 60 micrometers or less or equal to 50 micrometers. Inother embodiments, through-holes 309 have a characteristic diameter thatis less than or equal to 20 micrometers, less than or equal to 10micrometers, or less than or equal to 1 micrometer. The pitch betweenthrough-holes may be less than or equal to 125 micrometers, for example,less than or equal to 100 micrometers, less than or equal to 30micrometers, or less than or equal to 10 micrometers.

In certain embodiments, sample holder 304 comprises a substrate having athickness between the opposing surfaces of sample holder 304 that is ator about 300 micrometer, wherein each through-hole 309 may have a volumeof 1.3 nanoliter, 33 nanoliters, or somewhere between 1.3 nanoliter and33 nanoliters. Alternatively, the volume of each through-holes 309 maybe less than or equal to 1 nanoliter, for example, by decreasing thediameter of through-holes 309 and/or the thickness of sample holder 304substrate. For example, each through-holes 309 may have a volume that isless than or equal to 1 nanoliter, less than or equal to 100 picoliters,less than or equal to 30 picoliters, or less than or equal to 10picoliters. In other embodiments, the volume some or all of thethrough-holes 309 is in a range from 1 nanoliter to 20 nanoliters.

In certain embodiments, the density of through-holes 309 is at least 100through-holes per square millimeter. Higher densities are alsoanticipated. For example, a density of through-holes 309 may be greaterthan or equal to 150 through-holes per square millimeter, greater thanor equal to 200 through-holes per square millimeter, greater than orequal to 500 through-holes per square millimeter, greater than or equalto 1,000 through-holes per square millimeter, or greater than or equalto 10,000 through-holes per square millimeter.

Advantageously, all the through-holes 309 with an active area may besimultaneously imaged and analyzed by an optical system. In certainembodiments, active area comprises over 12,000 through-holes 309. Inother embodiments, active area comprises at least 25,000, at least30,000, at least 100,000, or at least 1,000,000 through-holes.

In certain embodiments, through-holes 309 comprise a first plurality ofthe through-holes characterized by a first characteristic diameter,thickness, or volume and a second plurality of the through-holescharacterized by a second characteristic diameter, thickness, or volumethat is different than the first characteristic diameter, thickness, orvolume. Such variation in through-hole size or dimension may be used,for example, to simultaneously analyze two or more different nucleotidesequences that may have different concentrations. Additionally oralternatively, a variation in through-hole 104 size on a singlesubstrate 304 may be used to increase the dynamic range of a process orexperiment. For example, sample holder 304 may comprise two or moresubarrays of through-holes 309, where each group is characterized by adiameter or thickness that is different a diameter or thickness of thethrough-holes 309 of the other or remaining group(s). Each group may besized to provide a different dynamic range of number count of a targetpolynucleotide. The subarrays may be located on different parts ofsubstrate 304 or may be interspersed so that two or more subarraysextend over the entire active area of sample holder 304 or over a commonportion of active area of sample holder 304.

In certain embodiments, at least some of the through-holes 309 aretapered or chamfered over all or a portion of their walls. The use of achamfer and/or a tapered through-holes have been found to reduce theaverage distance or total area between adjacent through-holes 309,without exceeding optical limitations for minimum spacing betweensolution sites or test samples. This results in a reduction in theamount liquid solution that is left behind on a surface of substrate 304during a loading process. Thus, higher loading efficiency may beobtained, while still maintaining a larger effective spacing betweenadjacent solution sites or test samples for the optical system.

In certain embodiments, system 1000 is configured to receive and processdifferent types or numbers of block 210, carrier 202, and/or sampleholder 204. For example, Thus, system 1000 may be configured to receiveand process different sample holders 204 having different numbers ofwells 209. Thus, system 1000 may be configured to receive and processsample holders 204 containing 96 samples and sample holders 204containing 48 wells and/or 384 well or/or more than 384 wells.Additionally or alternatively, system 1000 may be configured to receiveand process different sample formats or container configurations. Forexamples, in addition to receiving a sample holder 204 comprising apredetermined number of wells, system 1000 may also be configured toreceive and process one or more sample holders 304 comprising theplurality of through-holes 309. In certain embodiments, system 1000 isconfigured to receive and process four different types of sampleholders. Some of the characteristics of wells or through-holes used inthese four sample holders are listed in Table 1 below.

TABLE 1 Characteristics of four sample holders according to anembodiment of the present invention. Sample Sample Number ofCharacteristic Characteristic Holder Cell Type Cells Cell Volume CellDiameter A Well  96 200 microliters 5 millimeters B Well 384 50microliters 3 millimeters C Cavity 384 2 microliters 3 millimeters DThrough- 4 × 3072 0.033 microliters 0.35 millimeters hole

Referring again to FIGS. 1-3, optical sensor 118 may comprise one ormore photodetectors or photosensors, for example, one or morephotodiodes, photomultiplier tubes, or the like. Alternatively, opticalsensor 118 may comprise a one-dimensional or two-dimensionalphotodetector array 164, such as a charge-coupled device (CCD),complementary metal-oxide-semiconductor (CMOS), or the like. In theillustrated embodiment in FIG. 1, photodetector array 164 comprises atwo dimensional array of photosensitive pixels defining photosensitivesurface upon which an optical image or signal may be formed by emissionoptical system 125.

Excitation source 110 may be a halogen lamp, a Xenon lamp,high-intensity discharge (HID) lamp, one or more light emitting diodes(LEDs), one or more laser, or the like. In certain embodiments,excitation source 110 comprises a plurality of light sources havingdifferent emission wavelength ranges to excite different fluorescentdyes in biological samples 115, for a example, a plurality of LED lightsources having different colors or emission wavelength ranges. In suchembodiments, excitation filter assembly 132 may be omitted or may beincorporated for use with at least some of the different light sourcesto further limit the wavelength range of light or radiation reachingsamples 115.

In certain embodiments, excitation source 110 comprises one or morebroadband or white light LED sources. For example, excitation source 110may comprise a high power, broadband source having at least 5 watts oftotal output optical power, at least 10 watts of output optical power,or at least 25 watts of output optical power. In such embodiments,excitation filter assembly 132 may be incorporated to limit or definethe spectral content of the radiation or light received by samples 115and/or sample holder 204, 304. The spectral content of the broadbandsource 110 may be configured to favorably provide more energy overwavelength ranges that, for example, correspond to probes or dyemolecules in samples 115 that are less efficient, are typically foundlower concentrations, or otherwise require more photonic energy thatother dyes contained in samples 115.

In a non-limiting example, in certain embodiments, excitation source 110comprises a single broadband LED having a total optical power of greaterthan 10 watts over the spectral range produced by the LED. The spectraloutput characteristics of such an excitation source is shown by thesolid line in the graphs shown in FIG. 8. The horizontal axiscorresponds to the wavelength of radiation emitted by the LED excitationsource 110, while the vertical axis is a relative output intensity. The“relative intensity” for the plot in FIG. 8 is a percentage value thatis defined as 100 times the intensity measured at a given wavelengthdivided by the maximum intensity measured at any wavelength within rangeof wavelengths produced by the LED. For example, according to the plotin FIG. 8, the measured intensity out of the LED at a wavelength of 450nanometer is about 80 percent of the maximum intensity, where themaximum measured intensity occurs at an output wavelength of 457nanometers. By way of comparison, similar data for a halogen lamp usedin a prior art system is also shown in FIG. 8 as dashed lines. The setsof double lines with numeral in between indicate the approximatetransmission wavelength bands for the excitation filters shown in FIG.3.

For the illustrated embodiment shown in Table 1, the characteristic celldiameter and volume of sample holder D is much smaller than that ofsample holders A-C. As a result, a typical fluorescence signal producedby sample holder D is much smaller than a typical fluorescence signalproduced by sample holders A-C under similar conditions, for example,when using biological samples containing similar concentrations of abiological test sample and/or a fluorescent probe or reference dye. Forthese reasons, the halogen excitation source shown in FIG. 8 may notprovide sufficient intensity or power density for fluorescent probes ordyes excited by light in the wavelength range provided by filters 1-3 inFIG. 3.

In certain embodiments, fluorescent probes or dyes excited by light inthe wavelength range provided by excitation filters 1, 2, and 4 in FIG.3 are either more commonly used or are of greater importance than thoseexcited by light in the wavelength range provided by filters 3, 5,and/or 6, for example, in the wavelength range provided by eitherfilters 5 or 6. For example, in certain embodiments, the dyes FAM™ VIC®,and ROX™ are used, which dyes are commercially available from LifeTechnologies in Carlsbad, Calif. In such embodiments, excitation filter1 is used to excite the dye FAM™, excitation filter 2 may be used toexcite the dye VIC®, and excitation filter 4 may be used to excite thedye ROX™. Additionally or alternatively, it may be that fluorescentprobes or dyes excited by light in the wavelength range provided byfilters 3, 5, and/or 6 are not used with all types of sample holders A-Dand/or with all types of sample holders 204, 304, for example, are notused with sample holders D and/or sample holder 304. In such embodimentsas these, an excitation source 110 comprising an LED source havingspectral characteristics the same or similar to those shown in FIG. 8has an unexpected benefit, even though (1) the spectral power orintensity of the LED source for fluorescent probes or dyes excited bylight in the wavelength range provided by filters 5 and 6 is less thanthat for the halogen source shown in FIG. 8, and (2) the spectral poweror intensity of the LED source for fluorescent probes or dyes excited bylight in the wavelength range provided by filters 5 and 6 is less thanthat for fluorescent probes or dyes excited by light in the wavelengthrange provided by filters 1, 2, and/or 4. It has been discovered that,due to the relatively large sample volumes provided by the sample cellsin sample holders A-C, an LED source such as that characterized in FIG.8 is able to provide enough excitation energy to the biological samplesso that system 1000 is able to process the signals or images received byoptical sensor 118.

Accordingly, it has been discovered that instrument or system 1000 canprocess biological samples to provide useful data using a broadband LEDthat produces light or radiation having a maximum intensity and/or powerdensity at a wavelength that is less than 600 nanometers and/or that isless than 550 nanometers. For example, instrument or system 1000 canprovide useful PCR data (e.g., qPCR and/or dPCR data) using such abroadband LED, such as that represented in FIG. 8. The result is aninstrument that can provide data, such as PCR data, over a wide range ofsample sizes and sample holder or cell formats, for example, all thesample sizes and sample cell formats listed in Table 1.

In certain embodiments, system 1000 includes an excitation source 110comprising an LED having a spectral profile characterized by a maximumintensity or optical output power at a wavelength that is less than 550or 600 nanometers and an intensity or optical output power that is lessthan 50 percent the maximum value at a wavelength of 650 nanometerand/or 670 nanometers. In other embodiments, system 1000 includes anexcitation source 110 comprising an LED having a spectral profilecharacterized by a maximum intensity or optical output power at awavelength that is less than 550 or 600 nanometers and an intensity oroptical output power that is less than 30 percent or less than 20percent the maximum value at a wavelength of 650 nanometer and/or 670nanometers. In certain embodiments, the system 1000 further comprise anemission optical system 125 that is able to provide useful biologicaldata (e.g., PCR data) for sample cells having a diameter of less than500 micrometer, less than 200 micrometers, or less than 100 micrometersthat contain fluorescent probes or dye molecule that fluoresce atexcitation wavelengths that are less than or equal to 560 nanometer,while also being able to provide useful biological data (e.g., PCR data)for sample cells having a diameter of greater than 2 millimeters orgreater than 3 millimeters that contain fluorescent probes or dyemolecule that fluoresce at excitation wavelengths that are greater thanor equal to 620 nanometer or greater than or equal to 650 nanometers.

When used an system 1000 according to embodiments of the presentinvention, another unexpected advantage of an LED as described in theprevious paragraph and/or as illustrated in FIG. 8 is that infrared (IR)emissions from excitation source 110 are much lower than, for example, ahalogen light source according to that shown in FIG. 8. Thus,embodiments of the present invention provide reduced IR noise withoutthe need extra optical element such as so-called “hot mirrors” to blockIR emissions.

In certain embodiments, the output intensity, power, or energy ofexcitation source 110 may be varied depending on a condition or variablevalue, for example, depending on the type of sample holder used, size ofone or more reaction regions, experiment or run conditions of system orinstrument 1000, experiment or run conditions of optical system 100,experiment or run conditions of sample processing system 200, or thelike. For example, excitation source 110 may be an LED light source inwhich the output intensity, power, or energy is varied depending on oneor more of the conditions and/or variable values. In such embodiments,the output intensity, power, or energy of the LED may be varied byadjusting or changing a current or voltage driving the LED, and/or byadjusting or changing a duty cycle of the LED. In certain embodiments,the output intensity, power, or energy of excitation source 110 ischanged depending on the type of sample holder being used in system1000. For example, in certain embodiments, excitation source 110 may bean LED that is run at full output power, intensity, or energy—or at ahigher power setting output power, intensity, or energy—when sampleholder A from Table 1 is used. By contrast, the LED may be run at alower output power, intensity, or energy when a different sample holderis used, for example, sample holder B, C, or D from Table 1 is used.Such an arrangement allows system 1000 to provide emission data for thesmaller sample volume sizes and/or lower sample concentrations thatoccur when sample hold A is used, while also avoiding a saturation ofoptical sensor 118 when other larger sample volumes and/or higher sampleconcentrations are used.

Lens 152 is configured to form an image on photodetector array 164, forexample, by focusing collimated radiation entering from a particulardirection to a spot or point, for example, to a diffraction limited spotor a nearly diffraction limited spot. Lens 152 may be a simple lens,such as a plano-convex lens, plano-concave lens, bi-convex lens,bi-concave lens, meniscus lens, or the like. Alternatively, lens 152 maycomprise a compound lens such as a doublet lens or triplet lens thatmay, for example, comprise different lens materials selected to corrector reduce a chromatic aberration. In other embodiments, lens 152comprises system of lenses such as a camera lens system or microscopeobjective, for example, a commercially available camera lens. The cameralens system may be a commercially available camera lens comprising aconventional lens system design, for example, a double Gauss design, aCooke triplet design, retrofocus lens design (e.g., Distagon lensdesign), a Tessar lens design, or the like.

Lens 154 may be a single field lens, for example, configured to providea telecentric optical system when combined with the remaining opticalelements of excitation optical system 120 and/or emission optical system125. In such embodiments, lens 154 may be a simple lens, such as aplano-convex lens, plano-concave lens, bi-convex lens, bi-concave lens,meniscus lens, or the like. Alternatively, lens 152 may comprise adoublet lens or triplet lens, for example, comprising different lensmaterial to correct for a chromatic aberration. Additionally oralternatively, lens 154 may comprise a Fresnel lens or a diffractiveoptical element, surface, or pattern. In certain embodiments, lens 154may comprise a lens system, for example, a field lens in combinationwith an additional lens or lenslet array configured to focus lightwithin a sample well of sample holder 204. The lenslet array maycomprise a Fresnel lens or a diffractive optical element, surface, orpattern. Examples of such lens configurations are also describe in U.S.Pat. No. 6,818,437, which is herein incorporated by reference in itsentirety as if fully set forth herein.

Referring to FIG. 9, in certain embodiments, heated lid 212 comprises alenslet array 166, for example, for use with sample holder 204 (e.g.,like sample holders A-C listed in Table 1) for focusing light fromexcitation beam 111 into a well or cavity of a sample holder, such assample holders 204 in the illustrated embodiment. With additionalreference to FIG. 10, heated lid 212 may additionally or alternativelycomprise an optical window 167 for providing thermal isolation orimproved thermal performance of the thermal environment in or around asample holder, such as sample holder 304 in the illustrated embodiment.In certain embodiments, convective current can be produced when window167 is not located as shown in FIG. 10. Such convective heat flow hasbeen found to result in higher temperature or thermal non-uniformity(TNU) in substrate 306, in sample holder 304, and/or between samples 315than may be acceptable in some applications. Accordingly, placement ofwindow 167 between lens 154 and sample holder 304 can decrease theamount of convective currents around sample holder 304 and lead to adecreases in TNU.

Optical window 167 may be used in addition to or in place of opticalwindow 162 shown in FIG. 1. Either or both windows 162, 167 may bedisposed parallel to a surface of sample holder 304 and/or perpendicularto optical axis 170. Alternatively, one or both windows 162, 167 may bedisposed at an angle relative to a surface of sample holder 304 and/orat an acute angle to optical axis 170, for example, to reduceretro-reflections of light from excitation beam 111 back toward opticalsensor 118. One or both windows 162, 167 may comprise an antireflectivecoating to reduce retro-reflections of light from excitation beam 111back toward optical sensor 118. The antireflective coating may be usedin addition to, or as an alternative to, tilting one or both windows162, 167. Thus, system 1000 is able to accommodate and provide usefulbiological data (e.g., PCR data) for sample holders having a diversityof optical requirements by providing heated lids 212 having differentoptical characteristics from one another and/or serving differingthermal requirements for sample holders, such as sample holders 204, 304(e.g., sample holders A-D listed in Table 1).

In certain embodiments, the combination of lenses or lens systems 152,154 is selected to provide a predetermined optical result or imagequality. For example, in order to reduce system cost or to simplify theemission optical system 125 design, lens 152 may comprise a commerciallyavailable camera lens. Such lenses can provide very high image quality(e.g., images with low chromatic and monochromatic aberration) undercertain viewing conditions. However, the careful balance of higher orderaberrations incorporated into such camera lens design used to providesuch high image quality can be disturbed with the introduction of otherlenses into an imaging system. For example, in the illustratedembodiment shown in FIG. 1, a field lens such as lens 154 is added toemission optical system 125. Lens 154 is common to both excitationoptical system 111 and emission optical system 125 to provide both agenerally more compact optical system and efficient transfer offluorescent energy from a sample to the detection system.

In prior art systems, a field lens having a plano-convex lens shape orfigure has been found to provide certain favorable characteristic inthis respect, for example, to provide a telecentric lens systemconfigured to provide even illumination over a large field of view.However, to provide an acceptably low level of optical aberrations, suchprior art systems also incorporate a custom camera lens design in orderto reduce overall system aberrations when used in combination theplano-convex field lens. In particular, due to the extended field ofview used to simultaneously image a large number of biological samples,the camera lens was designed to provide low amounts of field curvature.However, it has been discovered that the combination of a plano-convexlens with a conventional or commercially available camera lens canresult in large amounts of field curvature that are undesirable. It hasbeen further discovered that field curvature can be significantlyreduced by combining a biconvex field lens 154 with a conventional orcommercially available camera lens, as illustrated in FIG. 1. Thisresult is surprising, since a biconvex lens would normally be expectedto reduce overall image quality in a telecentric lens system. Forexample, it has been found that when lens 152 comprises a commerciallyavailable camera lens of a retrofocus design (e.g., a Distagon lensdesign), the amount of field curvature produced when field lens 154 is abiconvex lens is much smaller than the amount of field curvatureproduced when field lens 154 is a plano-convex lens.

Emission filter assembly 130 may comprise a first filter module 138characterized by a first optical power and a first filter 140 having afirst filter function or transmission range 140 a. In the illustratedembodiment, first filter function 140 a is shown as filter number 6 inthe table of FIG. 2 and is characterized by a first low-pass wavelength140L of 700 nanometers and a first high-pass wavelength 140H of 720 nm,so that light within this wavelength range is transmitted, or largelytransmitted, through the first filter 140, while light or otherelectromagnetic radiation outside this wavelength range is blocked, orsubstantially blocked, by first filter 140. The wavelengths listed inFIGS. 2 and 3 may represent the wavelengths at which the transmission ofa filter is one-half the maximum transmission of the filter over thetransmission wavelength range. In such cases, the difference betweenhigh-pass wavelength and the low-pass wavelength define a full width athalf maximum transmission (FWHM) range.

Emission filter assembly 130 also includes a second, and optionally athird, filter component, element, or module 142, 143. Second and thirdfilter modules 142, 143 are characterized by second and third filters145, 146 having a second and third filter functions or transmissionranges 145 a, 146 a. Either or both filter modules 142, 143 may have anoptical power that is the same as, or different from, the optical powerof first filter module 138. At least one of the filter modules 142, 143may have an optical power of zero, which power may in general be eitherpositive or negative. Filter functions 145 a, 146 a comprise second andthird low-pass wavelengths 145L, 146L second and third high-passwavelengths 145H, 146H, respectively, for example, as filter numbers 1and 5 in the table of FIG. 2. Second and third low-pass wavelengths145L, 146L may be different than the low-pass wavelength 140L and/or maybe different from one another. Similarly, second and third high-passwavelengths 145H, 146H may be different than the high-pass wavelength140H and/or may be different from one another. In the illustratedembodiment, the transmission wavelength bands for filters 140, 145, 146(wavelengths 140L to 140H, 145L to 145H, and 146L to 146H) do notoverlap; however, in other embodiments, there may be at least someoverlap in the wavelength bands between two or more of the filters inemission filter assembly 130. In certain embodiments, one or more offunctions 140 a, 145 a, 146 a may comprise a function that is differentthan the simple bandpass configuration illustrated in FIG. 2.

FIG. 3 illustrates various filters available for use with excitationfilter assembly 132.

In FIG. 1, excitation filter assembly 132 comprises three filters, forexample, filters 1, 2, and 6 in FIG. 3, which in use may correspond tofilters 1, 2, and 6 shown in FIG. 2 for emission filter assembly 130. Atleast some of the filter modules 133 of excitation filter assembly 132may have non-zero optical powers, which power may in general be eitherpositive or negative. Alternatively, all the filter modules 133 may havezero or about zero optical power. In certain embodiments, selection of aparticular filter module 133 is associated with a particular filtermodule 131 of filter assembly 130. Alternatively, filter modules 133,131 may be selected independently of one another.

In the illustrated embodiment shown in FIG. 1, only three filter modulesare shown for each filter assembly 130, 132; however, either or bothfilter assemblies may comprise more or less than three filter modules.For example, FIGS. 2 and 3 each show a total of 6 filters, each of whichfilters may be associated an optical power (not shown). In certainembodiment, either or both filter assemblies 130, 132 contain all sixfilters shown in the table shown in FIGS. 2 and 3, respectively.Alternatively, either or both filter assemblies 130, 132 may compriseless than six filters.

Filter functions 145 a, 146 a comprise respective second low-passwavelengths 145L, 146L that may be different than the first low-passwavelength 140L and may be different from one another. Each filter ofthe filters in emission filter assembly 130 or in excitation filterassembly 132 may comprise a transmission range of electromagneticradiation or light that is different and non-overlapping from theremaining filters of filter assembly 130 or filter assembly 132.Alternatively, two or more of the filters in filter assembly 130 or infilter assembly 132 may comprise transmission ranges of electromagneticradiation or light that at least partially overlap one another.

In certain embodiments, the optical power one more or more of filtermodules 131, or of each filter modules 133, is selected to compensatefor or reduce an optical aberration of the remaining optical elements ofemission optical system 125 or excitation optical system 120 over awavelength range of the filter being used. For example, in order toprovide a predetermined image resolution or quality for various of thefilter modules 131 at an image plane of optical sensor 118 or emissionoptical system 125, the optical powers of some or all of filter modules131 may be selected to compensate for or reduce a chromatic orsphero-chromatic aberration introduced by emission optical system 125over different filter wavelength ranges. Additionally or alternatively,one or more of filter modules 131 or of filter modules 133 may comprisea monochromatic aberration, such as spherical aberration, astigmatism,or coma, that is configured to alter, adjust, or reduce an overallaberration of emission optical system 125 or excitation optical system120.

In certain embodiments, the optical power or a monochromatic aberrationof one or more of filter modules 131 is configured to at least partiallycorrect or adjust an image or focus of sample holder 204 and/or of atleast some of the biological samples 115 in an image plane at or near adetection surface of optical sensor 118. For example, in the illustratedembodiment, the optical powers of filter modules 138, 142, 143 are alldifferent from one another, with third filter module 143 having anoptical power of zero or about zero. The optical power of filter modules138, 142 may be selected so that an effective focal length of emissionoptical system 125 is adjusted over the transmission wavelength range ofeach filter 138, 142 is the same or about the same as the effectivefocal length when filter 143 is located in the emission optical system125. Additionally or alternatively, the optical power of filter modules138, 142 may be selected so that the image quality produced whencorresponding filter 140, 145 is inserted into emission optical system125 is the same or similar to the image quality produced when filter 146is inserted into emission optical system 125. For example, the opticalpower for each filter module 131 may be selected so that images ofbiological samples 115 are the same size, or about the same size, foreach filter module 138, 142, 143. Additionally or alternatively, theoptical power for each filter module 131 may be selected so that amagnification and/or aberration of images of biological samples 115 arethe same, or about the same, for each filter module 131. In certainembodiments, two or more of the optical powers may be the equal to oneanother. In general filter modules 138 and/or 142 may have opticalpowers that are greater than zero or less than zero in order to providea desired correction or adjustment to the emission optical system 125and/or images produced therefrom.

Beamsplitter 160 may be configured to selectively reflect a large amountof emitted light or radiation from excitation source 110 that istransmitted through a selected excitation filter module 133 and thendirected toward sample holder 204, 304. For example, the coatedbeamsplitter 160 may comprise a dichroic reflector that is configured toreflect at least 95 percent or at least 99 percent of incident lighttransmitted through excitation filter module 133. The same coating forbeamsplitter 160 can additionally be configured to transmit a largeamount of emission light or radiation from biological samples 115, forexample, to transmit at least 90 percent or at least 95 percent of lightor radiation emitted by biological samples 115. In certain embodiments,a different beamsplitter 160 is associated with each different filtermodule 133, for example, by attaching the different beamsplitters 160 toexcitation filter assembly 132. In certain embodiments, only some of thebeamsplitters 160 are wavelength selective or dichroic beamsplitters,while others of beamsplitters 160 associated with some of excitationfilter modules 133 are not wavelength selective, for example, a 50/50beamsplitter that reflect 50 percent of incident radiation over a broadband of wavelengths. In such embodiments, excitation light or radiationnot reflected by a beamsplitter 160, but transmitted through thebeamsplitter 160, may be intercepted by an emission filter module 131and directed to optical sensor 118 in the form of noise.

In certain embodiments, noise from excitation light or radiationtransmitted through a beamsplitter 160 is reduced by reducing the sizeof the corresponding emission filter module 131. However, the sizereduction of the corresponding emission filter module 133 may be limitedso as to avoid loss of signal from at least some of the biologicalsamples 115, 315, for example, due to vignetting effects on the moreperipherally located samples. It has been discovered that a reduction inexcitation radiation noise can be accomplished without significant lossof emission radiation signal by configuring the emission filters to havea shape that is the same as, or similar to, the shape of the area ofsample holder 204, 304 containing samples 115, 315. For example, it canbe seen in FIG. 4, 5, or 7 that a rectangular arca is defined by anactive arca over which one or more of sample holders 204, 304 containsamples or sample cells within the field of view of optical sensor 118.In such cases, it has been found that a rectangular shaped emissionfilter 140, 145, 146 or emission filter module 138, 142, 143 providesreduced noise from excitation radiation transmitted through beamsplitter160, without a significant loss of emission signal from samples 115, 315or uneven illumination from samples over the entire area of sampleholders 204, 304. In certain embodiments, the rectangular emissionfilter 140, 145, 146 or emission filter module 138, 142, 143 has thesame, or a similar, aspect ratio as that defined by an active area ofsample holders 204, 304, by carriers 202, 302, or by area of samples115, 315 that are within the field of view or field of regard of opticalsensor 118. For example, the aspect ratio of a rectangular emissionfilter (e.g., filter 140, 145, and/or 146) or filter module (e.g.,filter module 138, 142, or 143) may be selected to be within 1 percent,5 percent, 10 percent, or 20 percent of the aspect ratio of the activearea of a sample holder (e.g., sample holders 204 or 304) or of a groupof sample holders (e.g., the four sample holder 304 shown in FIG. 7).

During operation, biological samples 115 are disposed in a sampleholder, for example in sample holder 204, sample holder 304, or thelike. Biological samples 115 may include one or more nucleotidesequences, amino acid sequences, or other biological macromoleculesincluding, but not limited to, oligonucleotides, genes, DNA sequences,RNA sequences, polypeptides, proteins, enzymes, or the like. Inaddition, biological samples 115 may include other molecules forcontrolling or monitoring a biological reaction including, but notlimited to, primers, hybridization probes, reporter probes, quenchermolecules, molecular beacons, fluorescent dyes, chemical buffers,enzymes, detergents, or the like. Additionally or alternatively,biological samples 115 may include one or more genomes, cells, cellularnucleuses, or the like.

Once the biological samples are loaded, one or more sample holders areloaded or mounted within system 1000. In the illustrated embodimentshown in FIG. 1, one or more sample holders are mounted in to carrier202 or 302, which in turn is received by block 210 system 1000 and maybe subsequently covered or secured by heated lid 212. As discussed aboveherein, block 210 and heated lid 212 may be removably mounted or securedwithin system 1000, for example, so either or both may be exchanged foranother block or heated lid that is configured for use with a particularsample holder or carrier. Once the sample holder has been received bysample processing system 200, optical system 100 is used to monitor ormeasure one or more biological reactions or processes.

Emission optical system 125 of optical system 100 comprises an opticalaxis 170. A first emission beam 172 of emission beams 119 is emitted bya first biological sample located at or near optical axis 170. Firstemission beam 172 passes through emission optical system 125 such thatat least a portion of the electromagnetic radiation from the sampleproduces a first sample image 173 at or near photodetector array 164that is on or near optical axis 170. A second emission beam 174 ofemission beams 119 is simultaneously emitted by second biological samplelocated at or near an outer edge location of the array of biologicalsamples 115. Second emission beam 174 also passes through emissionoptical system 125 such that at least a portion of the electromagneticradiation from the sample produces a second sample image 175 at or nearoptical sensor 118 that is displace from optical axis 170. Emissionbeams 172, 174 may be fluorescence beams produced by different probemolecules contained in the two respective samples in response toexcitation beam 111. Depending upon the particular excitation filtermodule 133 selected, emission beams 172, 174 have a wavelength orwavelength range corresponding to the particular probe molecule that isexcited by radiation from excitation beam 111 that is transmitted by theselected excitation filter module 133. For example, when filter number 1in FIG. 3 may be used to filter radiation from excitation beam 111 andused in combination with emission filter number 1 in FIG. 2 (filter 146of filter module 143 in FIG. 1) to transmit radiation from emissionbeams 172, 174 onto photodetector array 164. As discussed above herein,the combination of lenses 152, 154 may be selected to form images fromemission beams 172, 174 that is low in monochromatic aberrations, and inparticular has a low amount of field curvature. A lateral distance(e.g., in a direction normal to optical axis 170) between the first andsecond samples may be compared to a lateral distance between thecorresponding images produced by emission optical system 125 todetermine a transverse magnification for the system when filter 146 isbeing used.

In certain embodiments, for radiation within the transmission range ofemission filter 146, first and second beams 172, 174 are collimated ornearly collimated when they leave lens 154 and form images at or nearphotodetector array 164 that have relatively low monochromaticaberrations and define a base system magnification. During use, emissionfilter assembly 130 may be subsequently moved (e.g., translated orrotated) so that emission filter module 143 and filter 146 are replacedby emission filter module 138 and filter 140 so the filter 140 (filternumber 6 in FIG. 2) now becomes part of the emission optical system 125,as illustrated in FIG. 1. Optionally, excitation filter number 1 in FIG.3 may also be replaced with excitation filter number 6 along excitationbeam path 111. As a result of chromatic aberrations, for radiationwithin the transmission range of emission filter 140, first and secondbeams 172, 174 are no collimated, but are divergent when they leave lens154. Thus, beams 172, 174 form images 173, 175 at or near photodetectorarray 164 that are further away from a principal plane of lens 152 thanthe images formed when filter 146 is present in emission optical system125. To correct or compensate for this effective change in focal lengthof emission optical system 125 over the transmission wavelength range offilter 140, a lens or optic 178 with a net positive optical power isincluded in filter module 138.

The added optical power to filter module 140 and emission optical system125 may be provided by a singlet lens 178, as shown in the illustratedembodiment of FIG. 1. The lens may be a plano-convex lens, plano-concavelens, bi-convex lens, bi-concave lens, meniscus lens, or the like.Alternatively, lens 178 may comprise a compound lens such as a doubletlens or triplet lens that may, for example, comprise different lensmaterials selected to correct or reduce a chromatic aberration. Optic178 may additionally or alternatively comprise a diffractive opticalelement. Optic 178 may be either a separate optical element, as shown inFIG. 1, or combined with filter 140 to form a single element. Forexample, optic 178 and filter 140 may be bonded together along a commonoptical face. Alternatively, optic 178 and filter 140 be formed togetherfrom a single substrate, for example, formed from a filter materialhaving one or both optical surfaces that are curved and/or contain adiffractive optical pattern. In certain embodiments, optic 178 islocated in a different part of emission optical system 125 than shown inFIG. 1, for example, on or proximal lens 154, window 162, orbeamsplitter 160, or at a location between beamsplitter 160 and emissionfilter assembly 130.

In addition to changing the effective focal length of emission opticalsystem 125, filter 140 may also result in a change in transversemagnification for the system. For example, even when lens 178 isincluded in filter module 138, the lateral distance between images 173,175 may be different when filter module 138 is used than when filtermodule 143 is used. In addition, the change from filter module 143 tofilter module 140 may introduce or alter various monochromaticaberration of emission optical system 125, for example, a sphericalaberration and/or field curvature. Accordingly, optic 178 or filtermodule 138 may be configured to at least partially correct or compensatefor such differences or changes in magnification and/or in one or moremonochromatic aberrations relative to when filter module 143 is used. Incertain embodiments, system 1000 or electronic processor 300 may includeimage processing instructions to at least partially correct orcompensate for changes in magnification and/or in one or moremonochromatic aberrations introduced by the use of filter module 138into emission optical system 125. The image processing instructions maybe used in combination with, or in place of, corrective optic 178 to atleast partially correct or compensate for changes in produces by the useof filter 140 in place of filter 146, including changes in effectivesystem focal length, magnification, chromatic aberrations, and/or one ormore monochromatic aberrations such as defocus, spherical aberrations,or field curvature.

In certain embodiments, each filter module 131 is disposed, in its turn,along the emission optical path 128 at a location where emission beam119, or some portion thereof, is either diverging or converging, wherebyone or more of filter modules 138, 142, 143 alters the amount ofdivergence or convergence to correct or adjust an effective focal lengthof emission optical system 125 and/or a spot size at an image plane ofemission optical system 125. In such embodiments, an optical power of atleast one of filter modules 138, 142, 143 is non-zero (i.e., eitherpositive or negative) over at least the transmission wavelength range orfilter function of corresponding filter 138, 142, 143.

In certain embodiments, the optical power of one or more of filtermodules 131, or one or more of filter modules 133, is greater than zeroand less than one Diopter. For example, the optical power of one or moreof filter modules 131, or one or more of filter modules 133, is greaterthan zero and less than or equal to one-third of one Diopter, less thanor equal to one-quarter of one Diopter, or less than or equal toone-eighth of one Diopter. Thus, optical power adjustment, while greaterthan zero, may be relatively small, so that only sight adjustments aremade in the optical characteristics of the emission optical system 125for at least some of the filters 140, 145, 146. Such slight adjustmentin optical power in the emission optical system 125 for differentfilters have been found to provide important optical corrections,resulting images created at optical sensor 118 that allow for bettercomparison between image data at different excitation and emissionconditions.

While most of the discussion above has related to emission opticalsystem 125 and the associated filter module 131, it will be appreciatedthat embodiments of the present invention also encompass similartreatment, where appropriate, of excitation optical system 120 and theassociated filter module 133.

In the illustrated embodiment shown in FIG. 1, a non-zero optical powerfor some of filter module 131, 133 is provided by a separate lens.Alternatively, a filter module 131, 133 may comprise a single opticalelement having both an optical power and filter transmission function.In certain embodiments, the single optic is made of a single material.Alternatively, two or more materials or elements may be adhered, joined,or bond together to form a filter module. In certain embodiments, theoptical power may be provided by a diffractive or holographic opticalelement or surface. The diffractive or holographic element or surfacemay be configured to reduce the size or thickness of a filter module.Additionally or alternatively, the diffractive or holographic element orsurface may be configured to introduce a chromatic aberration that isused to reduce a chromatic aberration produced by the remaining elementsof optical systems 125 or 120. In yet other embodiments, one or more offilter assemblies comprises a Fresnel lens or a curved mirror.

In certain embodiments, filter assembly 130 and/or 132 comprise acarrousel configuration in which different filter modules 131 or 133 arerotated into and out of the emission optical path 128 or excitationoptical path 126, respectively. In certain embodiments, filter assembly130 and/or 132 comprises interchangeable optical elements havingdiffering optical powers and interchangeable filters having differingfilter functions, wherein the optical elements and filters areindependently selectable from one another.

First optical element 152 is disposed near the optical sensor and isconfigured to provide images of samples 115 and/or sample holder 200.First optic element 152 may be a simple lens, such as a plano-convex orbi-convex lens, or a commercially available camera lens, such as aDouble Gauss lens, Distagon lens, Angenieux retrofocus lens, Cooketriplet, or the like. In the illustrated embodiment, filter modules 131are located between beamsplitter 160 and optical element 152, proximaloptical element 152. Second optical element 154 may be located nearsample holder 200 and be configured to provide a telecentric opticalsystem for illumination of the plurality of biological samples 115.

The above presents a description of the best mode contemplated ofcarrying out the present invention, and of the manner and process ofmaking and using it, in such full, clear, concise, and exact terms as toenable any person skilled in the art to which it pertains to make anduse this invention. This invention is, however, susceptible tomodifications and alternate constructions from that discussed abovewhich are fully equivalent. Consequently, it is not the intention tolimit this invention to the particular embodiments disclosed. On thecontrary, the intention is to cover modifications and alternateconstructions coming within the spirit and scope of the invention asgenerally expressed by the following claims, which particularly pointout and distinctly claim the subject matter of the invention.

The following list of co-pending U.S. applications are hereinincorporated by reference in their entirely as if fully set forthherein:

U.S. Provisional Patent Application No. 61/541,453, filed on Sep. 30,2011.

U.S. Provisional Patent Application No. 61/541,515, filed on Sep. 30,2011.

U.S. Provisional Patent Application No. 61/541,342, filed on Sep. 30,2011.

U.S. Design patent application Ser. No. 29/403,049, filed on Sep. 30,2011.

U.S. Design patent application Ser. No. 29/403,059, filed on Sep. 30,2011.

U.S. Provisional Patent Application No. 61/541,495, filed on Sep. 30,2011.

U.S. Provisional Patent Application No. 61/541,366, filed on Sep. 30,2011.

U.S. Provisional Patent Application No. 61/541,371, filed on Sep. 30,2011.

U.S. Provisional Patent Application No. 61/564,027, filed on Nov. 28,2011.

U.S. Provisional Patent Application No. 61/660,343, filed Jun. 15, 2012.

What is claimed is:
 1. An instrument for biological analysis,comprising: an excitation source producing electromagnetic radiation; asample holder configured to receive a plurality of biological samples;an optical sensor configured to receive an emission from the biologicalsamples; an excitation optical system configured to directelectromagnetic radiation from the excitation source to the biologicalsamples; an emission optical system disposed along an emission opticalpath and configured to form an image of the biological samples at animage plane located on or proximal to the optical sensor; a plurality offilters having different transmission wavelength bands, the filtersbeing interchangeably located along the emission optical path; whereinthe image plane of the biological samples have the same location alongthe emission optical path when any one of the filters is located alongthe emission optical path.
 2. The instrument of claim 1, wherein theimage plane is located within 100 micrometers of a surface of theoptical sensor.
 3. The instrument of claim 1, further comprising asample array disposed within the sample holder, the sample arraycomprising the plurality of biological samples.
 4. The instrument ofclaim 3, wherein the image of the biological samples comprises aplurality of spots comprising emissions from corresponding ones ofbiological samples.
 5. The instrument of claim 1, wherein at least onefilter of the plurality of filters comprises a singlet lens such thatthe at least one filter has a non-zero optical power for electromagneticradiation transmitted through the at least one filter.
 6. The instrumentof claim 1, wherein the plurality of filters comprises: a first filtercomprising of a low-pass or high-pass wavelength filter having nooptical power.
 7. The instrument of claim 1, further comprising a filterassembly configured to selectively position a filter of the plurality offilters into the emission optical path.
 8. An instrument for biologicalanalysis, comprising: an excitation source producing electromagneticradiation; a sample holder configured to receive a plurality ofbiological samples, the sample holder extending over a rectangular areahaving a first aspect ratio of a first value; an optical sensorconfigured to receive an emission from the biological samples; anexcitation optical system configured to direct the electromagneticradiation from the excitation source to the biological samples; anemission optical system configured to direct electromagnetic emissionsfrom at least some of the biological samples to the optical sensor; arectangular emission filter disposed along an optical path between thesample holder and the optical sensor, the rectangular emission filterhaving a second aspect ratio of a second value; wherein the first valueis within twenty percent of the second value.
 9. The instrument of claim8, wherein first value is within five percent of the second value. 10.The instrument of claim 8, wherein the first value is the same as thesecond value.
 11. The instrument of claim 8, further comprising a secondrectangular emission filter having a third aspect ratio of a thirdvalue, wherein the first value is within twenty percent of the thirdvalue.
 12. The instrument of claim 8, wherein the rectangular emissionfilter comprises a singlet lens such that the rectangular emissionfilter has a non-zero optical power for electromagnetic radiationtransmitted through the filter.
 13. The instrument of claim 8, furthercomprising a second rectangular emission filter.
 14. The instrument ofclaim 13, further comprising a filter assembly configured to selectivelyposition the rectangular emission filter or second rectangular emissionfilter into the emission optical path.
 15. An instrument for biologicalanalysis, comprising: an excitation source producing electromagneticradiation; a sample holder configured to receive a plurality ofbiological samples; an optical sensor configured to receive an emissionfrom the biological samples; an excitation optical system disposed alongan excitation optical path and configured to direct the electromagneticradiation from the excitation source to the biological samples; anemission optical system disposed along an emission optical path andconfigured to direct electromagnetic emissions from the biologicalsamples to the optical sensor; wherein the excitation source comprisesan LED having a spectral profile with a maximum value equal to a maximumintensity or maximum optical output power at a wavelength that is lessthan 600 nanometers and by an intensity or an optical output power thatis less than 30 percent the maximum value at a wavelength of 670nanometers.
 16. The instrument of claim 15, wherein the excitationsource comprises an LED having a spectral profile with a maximumintensity or optical output power at a wavelength that is less than 550nanometers and an intensity or optical output power that is less than 30percent the maximum value at a wavelength of 650 nanometers.
 17. Theinstrument of claim 15, further comprising a plurality of filtercomponents, the plurality of filter components comprising: a firstfilter component having no optical power, the first filter componentcomprising of a first filter characterized by at least one of (a) afirst low-pass wavelength or (b) a first high-pass wavelength.
 18. Theinstrument of claim 17, further comprising a filter assembly configuredto selectively position a filter component of the plurality of filtercomponents into the emission optical path.
 19. The instrument of claim15, further comprising a plurality of filters wherein at least onefilter of the plurality of filters comprises a singlet lens such thatthe at least one filter has a non-zero optical power for electromagneticradiation transmitted through the at least one filter.
 20. Theinstrument of claim 17, wherein the sample holder has a first aspectratio having a first value; and the plurality of filter componentscomprises a rectangular emission filter having a second aspect ratio ofa second value, wherein the first value is within twenty percent of thevalue second value.